In the design of high speed, open water boats, the deep Vee hull form is often preferred. Commonly, such hull forms are configured from keel to chine in one or more sections, with generally horizontal, longitudinally extending strakes being formed at transition areas to provide running surfaces. U.S. Pat. Nos. 3,415,213 and 5,063,868 are examples of such hull forms.
When operating at relatively high speeds, with the hull planing along the surface of the water, the frictional drag of the wetted surface of the hull is a significant speed-limiting factor. Accordingly, it is known to provide one or more steps in the hull form such that, as the boat achieves planing speeds, portions of the hull bottom are elevated above the water surface, reducing frictional drag and allowing higher planing speeds to be achieved. Examples of such stepped hull designs are reflected in U.S. Pat. Nos. 4,027,613, 4,231,314, 4,843,988, 4,903,626 and 4,958,585. All the foregoing examples show single-stepped hulls. It is also known to provide multiple steps. In some cases, the keel area of the hull has been recessed, as in U.S. Pat. No. 4,903,626, and in other examples, outer portions of the hull have been recessed at the step, as in U.S. Pat. No. 4,843,988.
The present invention is directed to a high speed hull form capable of operating at the higher limits of boat speeds and in a manner to both minimize running friction between the hull bottom and the water surface and to stabilize and improve the support of the hull by the water at high running speeds. The improved hull form achieves higher running speeds, while at the same time providing a safer and more comfortable ride.
In accordance with a significant feature of the invention, the hull bottom of a high speed watercraft, having a basic deep Vee hull form, is provided with two or more vertical steps in the fore-and-aft direction. In addition, and in combination, the hull is provided in the steps with variable dead rise from keel to chine in that, at each of the steps in the fore-and-aft direction, the height of the step in the region of the keel is greater than the height of the step in the region of the chine. Accordingly, as the vessel achieves planing speeds, ventilation occurs at the regions aft of the steps in a manner already known. In addition, because the areas of the hull bottom in the region of the keel, aft of the steps, is elevated to a greater extent than the bottom surfaces adjacent to the chines, the hull becomes supported to a greater extent in the areas adjacent to the chines and to a lesser extent in areas adjacent to the keel. This simultaneously reduces wetted surface area, and therefore running friction, and also stabilizes the hull against lateral rocking and chine walking, by supporting the hull more from laterally outwardly spaced areas, and less in central areas of the hull.
In accordance with another preferred embodiment of the invention, the attitude of the hull bottom in the areas of the multiple steps is altered slightly relative to the lines of the hull bottom immediately forward of the steps. Thus, the hull surfaces after the first step may be angled upwardly (fore-to-aft) at about one half degree relative to the lines of the hull bottom immediately forward of the step. Likewise, the attitude of each subsequent step, going aft, may be altered slightly (e.g., one half degree, upwardly fore-to-aft) relative to the bottom lines of the adjacent forward step.
In an optimum configuration, the beam of the hull chine increases substantially continuously from bow to transom. This provides additional lateral stability when running under high speed planing conditions, while allowing the narrowed bow and mid sections of the hull to effectively slice through waves.
The combination of multiple steps and variable dead rise, as described, has multiple advantages. It allows for a flatter running angle of the boat while at the same time providing for reduced drag and a concomitant increase in speed, and also improved longitudinal stability. Improved transverse stability is realized by the variable dead rise configuration at each step, elevating the keel areas relative to the chine areas. Hull forms according to the invention can be operated safely and effectively at speeds in excess of 100 miles per hour.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention and to the accompanying drawings.